(1) Field of the Invention
The present invention relates to a ceramic plate, more particularly, to a ceramic substrate or a ceramic package carrying a semiconductor element such as an IC and LSI.
(2) Description of the Related Art
Ceramic plates used for carrying semiconductor elements are normally alumina (Al.sub.2 O.sub.3 sintered plates, which have a superior strength, insulation, and chemical stability; i.e., a ceramic package is produced by using alumina as the raw material, (for example, cf. Tonegawa, Hirao and Takami, "Ceramic Package for LSI's", Denshi Zairyo (Electronic Parts and Materials), Vol. 16, No. 2, February 1977, Kogyo Chosakai, pp. 75-80 and 32, and Kumazawa, Ohno and Nomura, "Trends in Ceramic Packaging" Denshi Zairyo, Vol. 21, No. 8, August 1982, Kogyo Chosakai, pp. 52-57).
Recently, the integration degree and the operating speed of a semiconductor element (e.g., an LSI chip) have increased, and particularly in the case of an increase in the operating speed, preferably a dielectric constant of a ceramic material is as low as possible. A conventional alumina ceramic plate, however, has a relatively high dielectric constant (e) of from about 9 to 10, and since a high frequency signal propagation delay-time is proportional to a square root of the dielectric constant, the alumina ceramic plate has an adverse effect on the high frequency signal propagation speed. Accordingly, there is a need for a ceramic plate having a dielectric constant lower than that of the alumina ceramic plate.
Furthermore, there is a relatively large difference between the thermal expansion coefficients of the alumina ceramic plate and a semiconductor (silicon) chip, and when the size of the semiconductor chip is increased, stress is generated in the chip and in a connecting part between the chip and the ceramic plate, causing problems to arise during operation. Therefore, there is also a need for a ceramic plate having a thermal expansion coefficient closer to that of silicon than that of alumina ceramic plate.